reserve MS for non empty MidStr;
reserve a, b for Element of MS;
reserve M for MidSp;
reserve a,b,c,d,a9,b9,c9,d9,x,y,x9 for Element of M;
reserve p,q,r,p9,q9 for Element of [:the carrier of M,the carrier of M:];
reserve u,v,w,u9,w9 for Vector of M;
reserve X for Subset of [:the carrier of M,the carrier of M:];
reserve x for set;
reserve u1,v1,w1,W,W1,W2,T for Element of setvect(M);

theorem
  0.vectgroup(M) = zerovect M;
